Rotary drag bits have been used for subterranean drilling for many decades, and various sizes, shapes, and patterns of natural and synthetic diamonds have been used on drag bit crowns as cutting elements, or cutters. When drilling certain subterranean formations, a properly designed drag bit can provide an improved rate-of-penetration (ROP) over a tri-cone bit.
Rotary drag bit performance has been improved significantly with the introduction of polycrystalline diamond compact (PDC) cutting elements, usually configured with a substantially planar PDC table formed onto a cemented tungsten carbide substrate under high-temperature and high-pressure conditions. PDC tables are formed into various shapes, including circular, semicircular, and tombstone, which are the most commonly used configurations. Additionally, the PDC tables can be formed so that a peripheral edge, or edge portion, of the table is coextensive with the sidewall of the supporting tungsten carbide substrate, or the PDC table may overhang the substrate sidewall slightly, forming a “lip” at the trailing edge of the table. In some instances, such as when a portion of the PDC table adjacent the cutting face has been leached of the metal catalyst used to stimulate diamond-to-diamond bonding during formation of the PDC table, a lip may form during drilling due to more rapid wear of the unleached portion of the PDC table to the rear of the leached portion. PDC cutters have provided drill bit designers with a wide variety of potential cutter deployments and orientations, crown configurations, nozzle placements and other design alternatives not possible with natural diamond or smaller synthetic diamond cutters.
While rotary drag bits provide better ROP than tri-cone bits under many conditions, the performance of rotary drag bits can still be improved. Researchers in the industry have recognized that controlling buildup of recompacted rock cuttings, or detritus, on the cutting face of a PDC cutter is a significant factor affecting cutting performance. Methods used to manage detritus buildup on PDC table cutting faces include mechanical, hydraulic and chemical means of attacking the recompacted detritus.
The aforementioned lip configuration on PDC cutting elements has been observed to improve cutting efficiency by reducing detritus buildup on the sidewall of the cutting element to the rear of the PDC table, but the operative mechanism for this observed phenomenon has not been understood. Moreover, configuring a PDC cutting element with, or to form, a protruding lip adds cost to cutting element fabrication and the increased cost of such cutting elements may not be perceived to be commensurate with the benefits obtained for many applications.
What is needed are straightforward, cost-effective improvements to rotary drag bit cutters to inhibit flow and buildup of detritus over the side surface of the cutter adjacent the formation being cut, to remove recompacted detritus from the side surface of the cutter earlier in the buildup cycle, or both.